Autumn Nights Tend To Get Foggy

Written by: Scott Hetsko

Radiation fog is one of the most common types of fog. Radiation fog forms at night under a mainly clear sky and the air is calm. At night, the radiation balance of the surface is dominated by outgoing terrestrial (earth) longwave radiation. The lack of clouds enables much of the radiant energy to escape to space. As the surface loses energy it is cooled. The air in contact with the surface then begins to cool leaving the air aloft somewhat warmer. The cooling surface air reaches its dew point temperature and condensation begins to occur. Soon a cloud near the surface forms. Longer nights this time of year are perfect for radiation fog to form!